Adeno-associated viruses (AAVs) are small viruses which infect humans and some other primate species. AAVs are not currently known to cause disease and consequently the viruses cause a very mild immune response. Gene therapy vectors using AAV can infect both dividing and non-dividing cells and persist in an extrachromosomal state without integrating into the genome of the host cell. These features make AAVs very attractive candidates for creating viral vectors for gene therapy, and for the creation of isogenic human disease models.